Epilepsy is a disorder of the brain characterized by recurring seizures, in which there are uncontrolled electrical discharges of brain cells Epilepsy may arise from a very small area of damaged brain tissue or from the entire brain. There may be no apparent brain damage or damage may be limited to an area so small it cannot be detected. Therefore, in nearly one-half the cases, the cause of epilepsy is unknown
There are several types of seizures associated with epilepsy, the most common of which are generalized tonic-clonic (grand mal), absence (petit mal), complex partial (psychomotor), and elementary partial (focal motor). Each seizure type can be characterized by various symptoms. However, the seizures are generally not life threatening, lasting at most up to three minutes. The exception is status epilepticus, also called continuous seizure state. This is the occurrence of repetitive or continuous seizures and affects approximately 3 to 5% of those individuals suffering from epilepsy. It can exist with all types of seizures and may result in irreversible brain damage or death without prompt medical treatment.
One of the specific problems encountered by parents having children afflicted with epilepsy, particularly status epilepticus, is the problem of alerting the parents when the child may be having an epileptic seizure during sleeping hours. One recourse has been for the parents to sleep with the child, in the same bed, hoping to be awakened by the seizure during its early stages when the seizure motion may be quite mild. Often, the parents will choose to supplement this safeguard by using an alarm clock, set to sound every hour, to awaken and observe the state of the child. This, of course, places an extraordinary burden on both the child and the parents and is inherently unreliable as seizures may occur at any time. Moreover, the intermittent sleep afforded the parents as well as the desire for privacy by the child and by the parents make the procedure impractical and inefficient.
Motion sensor devices are obvious solutions to the aforementioned problem, provided that such devices be designed to ignore the casual motions of a sleeping child (rolling over, etc.) while responding to those motions characteristic of a seizure, however mild at the beginning. Existing motion sensor devices such as accelerometers or displacement followers could conceivably be designed to detect certain types of motion while ignoring others, but are invariably expensive, consume excessive power, and, when the required signal conditioning equipment is included, form a bulky package. Moreover, these devices commonly require electrical connections between the transducer (affixed to the patient) and its associated equipment located near, but not on, the patient.
One system has been proposed for use in monitoring children afflicted with status epilepticus, and is disclosed in a co-pending application having Ser. No. 08/443,911, filed May 18, 1995, which depends eventually, via an intermediate application (Ser. No. 08/312,853, filed Sep. 23, 1994) from an application having Ser. No. 08/154,324, filed on Nov. 18, 1993. In those applications, a hollow cylinder, capped at each end respectively by an electrically conductive circular plate that is electrically insulated from the cylinder such that the plates and cylinder are connected via an electronic circuit to DC voltage source. The plates are of the same polarity but opposite to the cylinder. An electrically conductive ball is placed in the cylinder and is free to roll to establish a closed electrical path at either end of the cylinder by being in contact with an end plate and the cylinder's interior surface. Electrical current makes and breaks are detected and monitored as the ball moves in a closed electrical path. When the predetermined pattern is detected, an alarm is sounded.
One of the major drawbacks of the proposed system has been the need to continuously update the voltage integral in time, and thus make continuous comparisons with alarm threshold criteria, allowing the effects of sensor variability to cause a large number of false alarms. If the parent or other person assigned to monitor the sleeping child is not allowed to rest, the device functionally has no value; thus false alarms are to be avoided if at all possible. Another drawback is that the prior art design does not always have contact between the sphere and the wall and the end cap of the cylinder.
Another drawback of the prior art system is that it required a ratio transmitter/receiver system that was not as reliable as desired, due in part to uncertainty over the battery reserve, and the chance that tuning was in error. Further, the lack of a backup alarm, and improper resetting after a false alarm were sources of unrelability.
Accordingly, it is an object of this invention to provide a device for sensing the motion of concern while ignoring, for the most part, other non-harmful motion such as ordinary movement during sleep.
Another object of this invention is to provide a monitoring device of the type described where the contact between the sphere, the wall and the end cap of the cylinder is increased in probability.
Still another object of this invention is to provide a monitoring device where the signal is received without need for tuning.
Yet another object of this invention is to provide a simple, effective device for monitoring epileptics without disturbing the sleep of the patient or the observer unless there is a need for concern.
Other objects will appear hereinafter.